1. Field of the Invention
The present invention relates to an illuminating device in which a fiber bundle, i.e. a bundle of optical fibers is used.
2. Description of the Related Art
A method for recording an image with a CCD camera and processing the image is well known in a measurement of the shape and size of a component, or an inspection of the presence of scratches and the appearance of a component, such as in an assembly line. In such a case, it is important to uniformly illuminate a subject without irregularities in illuminance level for an accurate measurement and inspection. Therefore, an illuminating device using an optical fiber bundle is conventionally used.
As shown in FIG. 10, the conventional illuminating device has a structure by which a surface to be illuminated 102 is illuminated with illuminating light from a light source 100 through a fiber bundle 101. In this device, it is possible to effectively utilize illuminating light by varying the shape of the emitting end portion of the fiber bundle 101 corresponding to the shape of the surface to be illuminated 102.
FIG. 11(a) is a facing view of the region illuminated by the conventional illuminating device shown in FIG. 10. FIG. 11(b) shows the illuminating light intensity distribution in a case of observing FIG. 11(a) from the direction designated by a and FIG. 11(c) shows the illuminating light intensity distribution in a case of observing FIG. 11(a) from the direction designated by C. These drawings show the occurrence of illuminance level irregularities. If such an illuminating device is incorporated in a liquid crystal display device or the like, it causes deterioration in the performance or quality of such products.
Japanese laid-open patent publication No. 9-146014 discloses prior art in which a diffusing plate, comprising a lens such as a lenticular lens, is positioned at the exit end of a fiber bundle. In this art, a magnifying lens is positioned at the exit end of the fiber bundle and a diffusing plate is positioned at the focal point of the magnifying lens, thereby the possibility of observation from various directions is achieved. However, in a device according to this art, illuminating light for illuminating a surface is not uniformly diffused.
According to the present invention, there is provided an illuminating device for illuminating a surface to be illuminated with light passed through a fiber bundle from a light source, wherein a microlens array is provided at the end surface of said fiber bundle to uniformly diffuse illuminating light for illuminating a surface to be illuminated or to make illuminating light converge on one portion.
As a light source, a halogen lamp, a metal halide lamp, a xenon lamp, and so on may be used. The wavelength thereof may be in the ultraviolet region and is not limited to light of the visible wavelength region. Further, it is preferable to obtain a light source by combining a lamp with an oval reflecting mirror. In a fiber bundle, either of a glass fiber or a resin fiber may be used. A microlens may be obtained by conducting an etching upon silica glass, an injection molding, a molding using photopolymers, or the like. Furthermore, a microlens may be positioned at the incident (light source) end of the fiber bundle or at the exit end of the fiber bundle.
In a specific structure of an illuminating device according to the present invention, the shape of the exit end of the fiber bundle is made linear or narrowly rectangular. A microlens array the shape of which corresponds to the shape of the exit end of the fiber bundle is positioned at the exit end of the fiber bundle. The microlens array comprises a lenticular lens. The longitudinal direction of each of microlenses which form the lenticular lens coincides with the shorter side of the exit end of the fiber bundle.
In another specific structure of an illuminating device according to the present invention, the shape of the exit end of the fiber bundle is made linear or narrowly rectangular. A microlens array the shape of which corresponds to the shape of the exit end of the fiber bundle is positioned at the exit end of the fiber bundle. A lenticular lens is formed on one surface of the microlens array, and a cylindrical lens is formed on the other surface of the microlens array. The longitudinal direction of each of microlenses which form the lenticular lens coincides with the shorter side of the exit end of the fiber bundle, and the longitudinal direction of the cylindrical lens coincides with the longer side of the exit end of the fiber bundle.
In another specific structure of an illuminating device according to the present invention, the shape of the exit end of the fiber bundle is made annular. An annular microlens array the shape of which corresponds to the shape of the exit end of the fiber bundle is positioned at the exit end of the fiber bundle. A surface to be illuminated is illuminated with light from this annular microlens array through an axicon lens.
In another specific structure of an illuminating device according to the present invention, the shape of the exit end of the fiber bundle is made rectangular. A rectangular microlens array the shape of which corresponds to the shape of the exit end of the fiber bundle is positioned at the exit end of the fiber bundle and is formed by densely arranging rectangular microlenses. In addition, each of the rectangular microlenses has different radiuses of curvature with respect to length and width, so that the angle of convergence and divergence of illuminating light is different with respect to length and width.